The present invention relates to an accelerator pump system for a carburetor of an internal combustion engine.
There have heretofore been known carburetors having an accelerator pump for supplying additional fuel to an engine upon acceleration to meet a demand for increased engine power. Such an accelerator pump also serves to provide a two-barrel carburetor with better transient conditions in which a secondary intake passage comes into operation in addition to a primary intake passage. It frequently happens that a car runs continuously for a certain period of time, is stopped with the engine turned off, and then the engine is restarted for acceleration. Under such a running condition, however, the accelerator pump and associated fuel passages are filled with fuel vapor due to percolation caused by heat of the engine while the car is held at rest. The fuel passages suffer from vapor lock which renders fuel feed less responsive. With a two-barrel carburetor having primary and secondary intake passages having a large ratio between their cross-sectional areas, the vapor lock gives rise to poor transient conditions in which the secondary intake passage comes into operation, resulting in hesitation or stumble and hence poor drivability.